Conventionally, glass powder has been widely used for adhering metal members together, ceramic members together, or a metal member with a ceramic member by melting the glass powder.
For example, since a solid oxide fuel cell usually requires an operation temperature of 800° C. to 1,000° C., glass known as crystallized glass has been used for the sealing between cells and metal members to be attached thereto.
More specifically, for example, such glass powder is used when producing a solid oxide fuel cell in the following manner. A glass powder is formed from a glass composition that can crystallize by sintering under predetermined temperature conditions. A sealing material containing this glass powder is filled between members that need to be sealable and the glass powder is sintered to have a sintered body formed from the crystallized glass formed between these members, thereby sealing them.
Since this type of crystallized glass generally exhibits little crystal phase transformation due to the sintering temperature, and has high thermal expansion properties and high strength, it can be said to be a material suitable for sealing a solid oxide fuel cell.
Regarding this point, for example, Patent Documents 1 and 2 mentioned below describe a glass composition with which the sintered crystallized glass exhibits a high thermal expansion coefficient even in a high temperature region, and describe that such a glass composition is suitable for application of sealing a solid oxide fuel cell.
A solid oxide fuel cell has cells in which an electrolyte material formed from a ceramic porous body is sandwiched by an anode material and a cathode material. Generally, a composite material of a nickel oxide and a ceramic is used as the anode material. As the cathode material, LSM (lanthanum strontium manganite), LSC (lanthanum strontium cobaltite), SSC (samarium strontium cobaltite), LSCF (lanthanum strontium cobalt ferrite) and the like are used.
Further, when trying to increase the power output by forming a stack obtained by laminating the cells thus constituted with an interconnector arranged between them, there is a case in which LSCF is used as the material forming the interconnector.
Therefore, for a glass composition used for sealing a solid oxide fuel cell, it is desirable to consider not only thermal expansion coefficient of the obtained glass, but also the reactivity with these materials.
However, studies on conventional sealing glass compositions showed that little consideration has been given to the reactivity with these materials, and there is no glass composition heretofore found, which suppresses the reactivity with the materials forming a solid oxide fuel cell, while at the same time having a thermal expansion coefficient suitable for sealing a solid oxide fuel cell.